The present invention relates to an electrostatic information recording medium and an electrostatic information recording and reproducing method, by which the information can be electrostatically recorded and reproduced at any desired time.
Conventionally, silver salt photographing method is already known as a technique for high sensitivity photographing. In this photographing method, the photographed image is recorded on film through the development process, and silver salt emulsion (such as photographic paper) is used for reproducing the image or it is reproduced on cathode ray tube (CRT) by optically scanning the developed film.
There is also an electronic photographing technique, in which an electrode is deposited on photoconductive layer by evaporation and the surface of photoconductive layer is electrically charged by corona charging in a dark place. Then, it is exposed to intensive light to make the exposed photoconductive layer electrically conductive. By removing the electric charge on that portion by leaking it to form electrostatic latent image on the surface of the photoconductive layer, and the toner is attached, which has an electric charge with a polarity opposite to that of the remaining electrostatic charge. This technique is mostly used for duplication purposes and is not generally suitable for photographing because of its low sensitivity. Since electrostatic charge retaining time is short, toner development is usually performed after the electrostatic latent image is formed.
Further, there is the method for TV photographing technique, in which photographing is performed by an image pickup tube and the image information obtained by an optical semiconductor are taken out as an electric signal. This is directly outputted on a CRT or is recorded on video by magnetic recording and the image is reproduced on a CRT when desired.
Also, a method is known, in which thermoplastic materials having an electric charge carrying property are laminated on a transparent electrode and selenium particles are deposited by vacuum evaporation on the surface of the thermoplastic material and is infiltrate to prepare the recording medium. To record the information on this recording medium, the surface of the thermoplastic material is electrically charged by corona charging, and the image is exposed to light by applying a voltage between the electrodes disposed at face-to-face positions. Thus, an optical carrier is generated on the photoconductive particles in the exposure portion to form the latent image. For the development, the thermoplastic material is softened by heating, and only the photoconductive particles generating an optical carrier are migrated in the thermoplastic material layer. The information thus developed is reproduced as visible information according to the quantity of transmission light (U.S. Pat. Nos. 3,520,681, 4,101,321 and 4,496,642).
The silver salt photographing method is an excellent means to preserve the image of the object, but it requires a development process to form the silver salt image and also the complicated optical, electrical and chemical processings are involved in reproducing the image to hard copy and soft copy (CRT output), etc.
The electronic photographing technique is more simple and quick than the silver salt photographing method in reproducing the electrostatic latent image, whereas the latent image can be preserved only for a short period, and the dissociation of the development, image quality, etc. are inferior to those of the silver salt method.
TV photographing technique requires linear sequential scanning to take out and record the electric image signals obtained by the pickup tube. Linear sequential scanning is performed by an electron beam in the pickup tube and by a magnetic head in video recording. Since resolution depends upon the number of scanning lines, it is extremely inferior to the planar analog recording such as in silver salt photographing.
The recently developed TV image pickup technique using solid-state image sensor (such as CCD) is also essentially the same with regards to the resolution.
The problems involved in these techniques lie in the fact that the processing becomes more complicated if higher quality and resolution are required in the image recording and the memory function is lacking or image quality is basically poor if the processing is simplified.
There is another technique, in which a thermoplastic material layer containing a selenium particle layer is provided on the transparent electrode and it is electrically (charged by corona charging. After the image is exposed, the thermoplastic material is softened and the image is heat-developed, and the information is reproduced as visible information. In this case, the electric charge information thus accumulated can be preserved for a long period (10 years or more), whereas the application is limited as an information recording means by a camera because corona charging is needed for information recording. Also, on the surface of the thermoplastic resin softened during heat development, the so-called frost phenomenon occurs, in which fine irregularities are caused by the repulsion between the surface electric charge, when it is electrically charged to a higher potential. As the result, when the accumulated information is detected as surface potential, noise occurs and the resolution is adversely affected.